This invention relates generally to cushioning the end of travel of a hydraulic actuator and more particularly to a cylinder snubbing arrangement that controls the rate of deceleration.
Linear fluid actuators, such as hydraulic cylinders, are well known in the art. It is a well known problem that if the cylinder is allowed to xe2x80x9cbottom outxe2x80x9d, that is the piston of the cylinder harshly impacts the bottom of the cylinder, damage can result from such impact. This damage may be to the cylinder or to components that the cylinder is connected. To reduce or eliminate such shocks, various types of end of stroke cushioning devices have been installed. One such device is set forth in U.S. Pat. No. 3,845,694 issued on Nov. 5, 1974 and assigned to Caterpillar Tractor Co. In this arrangement, small openings are provided in the cylinder body to direct pilot signals to a bypass valve that is operative to progressively restrict the flow from the end of the actuator and at the same time proportionally interconnect the ends of the cylinder. In the known cylinder snubbing arrangements, many modifications have been required within the cylinder body, piston, or rod or various complicated valving has been required. When a fluid cylinder is subjected to large differential pressures between the head end cavity and the rod end cavity, the life of the seals on the piston within the cylinder may prematurely leak or fail. It is desirable to provide an effective cylinder snubbing arrangement that is effective and simple in design.
The subject invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a snubbing arrangement is provided for a fluid cylinder assembly used in a fluid system of a machine having the fluid cylinder assembly connected between two members. The fluid cylinder assembly includes a piston and rod assembly that is slideably disposed within a cylinder housing to define head and rod end cavities and respective head and rod end fluid ports. The snubbing arrangement includes a flow blocking mechanism connected to the piston of the fluid cylinder and operative to engage and block fluid exiting the head end fluid port prior to the piston reaching the bottom of the head end cavity, a second head end port connected to the head end cavity generally adjacent the bottom thereof and spaced from the first head end port, and a pressure differential valve mechanism connected between the second head end port and the rod end port and operative to control the pressure of the fluid within the head end cavity relative to the pressure within the rod end cavity.